The present invention relates to a composite sheet for food containers for containing food or beverage which has excellent sealability, heat resistance, aroma proof and low-temperature impact resistance and which can be subjected to high-temperature sterilization.
Hitherto, as containers or packaging materials for packaging foods which are highly susceptible to oxygen gas without causing deterioration of the foods, synthetic resin containers or packaging materials prepared by the methods called vacuum forming or air-pressure forming from a laminate sheet of at most about 1 mm thick comprising polypropylene/ethylene-vinyl alcohol copolymer/polypropylene have been utilized as disposable containers.
These conventional containers have problems that they are not sufficient in aroma proof and flavor of foods is spoiled. For solving these problems, JU-B-5(1993)-8127 proposes to provide an aroma proof resin layer comprising a saturated polyester resin layer or polycarbonate resin layer as the innermost layer. According to this invention, there is obtained a container which can preserve foods without spoiling flavor by laminating in succession the aroma proof resin layer, a water vapor barrier resin layer, a gas barrier resin layer and a thermoplastic resin layer.
The flavor of foods is deteriorated with oxygen gas, and, besides, the flavor per se is adsorbed (absorbed) into the materials of containers or packaging materials or transmits through containers or the like, and thus the flavor of foods is spoiled. This causes deterioration of quality of contents. It is generally known that saturated polyester resins or polycarbonate resins are high in the effect to preserve the flavor.
The above-mentioned containers are filled with contents, sealed and heat treated in factories and then distributed to shops. Some of the commodities are stored at low temperatures during the stage of this distribution, and even in the case of distribution at room temperature, the temperature becomes considerably low in winter. The conventional containers lower in impact resistance during distribution at low temperatures, and cracks may occur in a part of the container. In this case, if the content is liquid, there is the possibility of the content leaking out of the container. Furthermore, there is the possibility of the content putrefying because gas barrier properties imparted to the container cannot be sufficiently exhibited.
Various proposals have also been made on containers improved in impact resistance at low temperatures, but composite sheets for food containers of high low-temperature impact resistance with having both the preservability and aroma proof of contents have not yet been disclosed.